Figure 6.12 An estimated tally of the ATP produced by substrate-level and oxidative phosphorylation in cellular respiration.

Fermentation captures significantly less energy from a glucose molecule than is captured from glucose through respiration. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). 4. Students may expect that fermentation will produce alcohol and maybe even carbon dioxide. Take the time to clarify the different possible products of fermentation and correct this general misconception. Teaching Tips 1. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the oxygen immediately above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish.

Fermentations are used by the dairy industry to make cheese and yogurt, while other industries produce soy sauce and sauerkraut through fermentation reactions. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). 4. Students may expect that fermentation will produce alcohol and maybe even carbon dioxide. Take the time to clarify the different possible products of fermentation and correct this general misconception. Teaching Tips 1. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the oxygen immediately above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish.

The carbon dioxide provides the bubbles in beer and champagne and also the bubbles in dough that cause bread to rise. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). 4. Students may expect that fermentation will produce alcohol and maybe even carbon dioxide. Take the time to clarify the different possible products of fermentation and correct this general misconception. Teaching Tips 1. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the oxygen immediately above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish.

Ancient prokaryotes probably used glycolysis to make ATP long before oxygen was present in Earth’s atmosphere. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips 1. The widespread occurrence of glycolysis, which takes place in the cytosol and independent of organelles, suggests that this process had an early evolutionary origin. Since atmospheric oxygen was not available in significant amounts during the early stages of Earth’s history, and glycolysis does not require oxygen, it is likely that this chemical pathway was used by the prokaryotes in existence at that time. Students focused on the evolution of large, readily apparent structures such as wings and teeth may have never considered the evolution of cellular chemistry.

Teaching Tips 1. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 lbs overweight, you would be nearly 40 lbs overweight if the same energy were stored as carbohydrates or proteins instead of fat). 2. Figure 6.15 is an important visual synthesis of the diverse fuels that can enter into cellular respiration and the various stages of this process. Figures such as this can serve as a visual anchor to integrate the many aspects of this chapter. 3. The final modules in this chapter may raise questions about obesity and proper diet. The Centers for Disease Control and Prevention website, www.cdc.gov/nccdphp/dnpa/, discusses many aspects of nutrition, obesity, and general physical fitness and is a useful reference for teachers and students.

Figure 6.15 Pathways that break down various food molecules.

Answer: 2

For BLAST Animation Building a Protein, go to Animation and Video Files. Student Misconceptions and Concerns 1. Many students may only view nutrients as sources of calories. As noted in Module 6.16, the monomers of many nutrients are recycled into synthetic pathways of organic molecules. Teaching Tips 1. The final modules in this chapter may raise questions about obesity and proper diet. The Centers for Disease Control and Prevention website, www.cdc.gov/nccdphp/dnpa/, discusses many aspects of nutrition, obesity, and general physical fitness and is a useful reference for teachers and students.

Figure 6.16 Biosynthesis of large organic molecules from intermediates of cellular respiration.

The electron transport chain is too deeply embedded in the mitochondria.

The electron transport chain only receives electrons carried by reduced electron carrier molecules such as NADH.

The electron transport chain only receives electrons carried by oxidized electron carrier molecules such as NAD+.

The electron transport chain does not produce ATP.

The figure above represents an overview of the different entry pathways to cellular respiration when different macromolecules are digested for energy production. Why are none of the digestive products entering the electron transport chain, directly?

The electron transport chain only receives electrons carried by reduced electron carrier molecules such as NADH.

The figure above represents an overview of the different entry pathways to cellular respiration when different macromolecules are digested for energy production. Why are none of the digestive products entering the electron transport chain, directly?